Cross-linked polyolefin tape

ABSTRACT

The invention relates to polymer tapes that are blends including at least one silane-grafted single-site initiated polyolefin resin. The silane-grafted single-site initiated polyolefin resin generally is a copolymer of ethylene and a C 3 -C 20  alpha-olefin that has a molecular weight distribution between about 1.5 and about 3.5. The polymer tapes include an adhesive on at least one face of the polymer. The polymer tapes can be foamed.

This is a divisional of application Ser. No. 08/639,357, filed Apr. 26,1999, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to cross-linked polyolefin resins used to carryadhesives, as in a tape.

In general, tape is useful in joining applications and can be formedfrom polymer resins with good flexibility properties that are coatedwith adhesives. Tapes can include foamed or non-foamed polymer resins.

Foamed tape is a useful in applications where cushioning or gap-fillingis important. Gap-filling is particularly important when the surface ofthe substrate is not uniform; the tape is capable of filling the surfaceirregularities and provide good contact of the adhesive surface with thesubstrate surface. Foamed tapes are useful for joining rough andirregular surfaces. It is important for the foamed tape to be flexible.

In tape applications, the surface of the polymer resin should be easilycoated with a film of the adhesive. It is also important that thepolymer resin adhere well to the adhesive in order to bond well to asubstrate surface. Generally, desirable foams for making foamed tapeshave low densities, decreasing the cost of material and weight whilemaintaining good foam properties. Foamed tapes can also have goodinsulating qualities.

In general, foamed tapes with these properties contain foams based onpolyvinylchlorides (PVC), ethylene-propylene-diene monomer (EPDM)terpolymers, polyurethanes, or radiation cross-linked polyolefinmaterials. These materials generally contain other additives, such asplasticizers, to add to their flexibility. Polyolefins alone aretypically limited in their application to adhesive tapes because oftheir limited flexibility. However, plasticizers can leach out of thematerials over time which can make the materials less flexible anddegrade the properties of the adhesives. In some circumstances, foamsfor use in tape applications should have good weatherability and flameresistance.

SUMMARY OF THE INVENTION

In general, the invention features polymer tapes that are blends of apolymer resin and a silane-grafted single-site initiated polyolefinresin. The silane-grafted single-site initiated polyolefin resingenerally is a copolymer of ethylene and a C₃-C₂₀ alpha-olefin that hasa molecular weight distribution between about 1.5 and about 3.5. Thepolymer tapes can be foamed to form foamed polymer tapes.

In one aspect, the invention features a polyolefin tape including apolyolefin sheet and an adhesive on at least one face of the sheet, thepolyolefin including a silane-grafted single-site initiated polyolefinresin. It is preferred that the tape have a thickness of less than about{fraction (5/16)} inch.

In other preferred embodiments, the polyolefin is foamed. It ispreferred that the foam have a 25% compression resistance of less than75 psi, more preferably less than 25 psi, and an elongation greater than100 percent, more preferably greater than 250 percent.

In another aspect, the invention features a polymer tape including anadhesive and a silane-grafted polymer blend containing at least onesingle-site initiated polyolefin resin, the polymer tape having atensile strength greater than 20 psi, a 25% compression resistancegreater than 3 psi, more preferable between 3 and 150 psi, and anelongation greater than 100 percent, more preferably greater than 250percent.

In preferred embodiments, the polymer blend is foamed. Preferably, thefoam has a density between 1.5 and 50 pounds per cubic foot.

In preferred embodiments, the silane-grafted single-site initiatedpolyolefin resin is a copolymer of ethylene and a C₃-C₂₀ alpha-olefinhaving a density between about 0.85 and 0.91 g cm⁻³ and a molecularweight distribution between about 1.5 and about 3.5. In other preferredembodiments, the polymer blend is foamed. It is preferred that a portionof the single-site initiated polyolefin resin be silane-grafted.

In preferred embodiments, a portion of the polyolefin, or polymer blend,is cross-linked. In other preferred embodiments, the polyolefin, orpolymer blend, contains greater than about 20 percent silane-graftedsingle-site initiated polyolefin resin. It is preferred that thesilane-grafted single-site polyolefin resin contain between about 0.1and 3 percent silane.

In preferred embodiments, the tape further includes a polyethylene resinor an ethylene-vinyl acetate copolymer resin. It is preferred that thepolyolefin tape contain between 20 and 50 percent ethylene-vinyl acetatecopolymer resin. It is preferred that the ethylene-vinyl acetatecopolymer resin contains between 5 and 25 percent vinyl acetate.

In other preferred embodiments, the silane includes a vinyl silane with2 or 3 hydrolyzable groups. It is preferred that the adhesive include arubber adhesive or an acrylate adhesive.

In yet another aspect, the invention features a method of making apolymer tape including the steps of: providing a cross-linkable polymermixture including at least one single-site initiated polyolefin resinand a chemical foaming agent; extruding the polymer mixture; andapplying an adhesive to the polymer mixture.

In preferred embodiments, the method further includes the step ofsilane-grafting the polymer mixture. In other preferred embodiments, themethod further includes the step of silane-grafting the single-siteinitiated polyolefin resin.

It is preferred that the method further include the step of expandingthe polymer mixture to form a foam. Preferably, the method also includesthe step of cross-linking the polymer mixture. It is preferred that thestep of cross-linking the polymer mixture include exposing the polymermixture to moisture.

The term “short-chain branching,” as used herein, means a branch of apolymer backbone of 6 carbon atoms or less which can be distinguished by¹³C NMR spectroscopic methods.

The term “copolymer,” as used herein, means a polymer resulting from thepolymerization of two or more monomeric species, including terpolymers(e.g., resulting from the polymerization of three monomeric species),sesquipolymers, and greater combinations of monomeric species.Copolymers are generally polymers of ethylene with C₃-C₂₀ alpha-olefins.

The densities, or specific gravities, of the polymer resins can bemeasured using ASTM D-792 methods.

The phrase “single-site initiated polyolefin resin,” as used herein,means a polyolefin prepared from a single-site initiated polyolefin thathas controlled molecular weights and molecular weight distributions. Thepolyolefin can be polyethylene, polypropylene, or a copolymer ofethylene and alpha-unsaturated olefin monomers. One class of asingle-site initiators of particular interest are the metalloceneinitiators which are described, for example, in J. M. Canich, U.S. Pat.No. 5,026,798, in J. Ewen, et al., U.S. Pat. No. 4,937,299, in J.Stevens, et al., U.S. Pat. No. 5,064,802, and in J. Stevens, et al.,U.S. Pat. No. 5,132,380, each of which are incorporated herein byreference. These initiators, particularly those based on group 4transition metals, such as zirconium, titanium and hafnium, areextremely high activity ethylene polymerization initiators.

The single-site initiators are versatile. The polymerization conditionssuch as a initiator composition and reactor conditions can be modifiedto provide polyolefins with controlled molecular weights (e.g., in arange from 200 g mol⁻¹ to about 1 million or higher g mol⁻¹) andcontrolled molecular weight distributions (e.g., M_(w)/M_(n) in a rangefrom nearly 1 to greater than 8, where M_(w) is the weight averagemolecular weight and M_(n) is the number average molecular weight).Molecular weights and molecular weight distributions of polymers can bedetermined, for example, by gel permeation chromatography.

The polyolefins provided by these initiators are essentially linear,meaning that the polymers can contain uniformly distributed, highlycontrolled short chain branching sites. As used herein, the term“essentially linear” means that the polymers have less than about onelong-chain branch for every ten thousand carbon atoms in the backbone ofthe polymer. As described above, one method of determining branching is¹³C NMR spectroscopy.

When the single-site initiated polyolefins are copolymers, thecomposition distribution breadth index (CDBI) is generally greater than50% and most preferably above 70%. The CDBI is a measurement of theuniformity of distribution of commoners among the individual polymerchains having a commoner content within 50% of the median bulk molarcommoner content.

The “melt index” (MI) of a polymer resin is a measurement ofprocessability under low shear rate conditions. The MI can be determinedby ASTM D-1238 Condition E (190° C./2.16 kg). The MI of the polyolefinsis generally between about 0.2 dg/min and about 100 dg/min, preferably,between about 1 dg/min and about 10 dg/min, and most preferably betweenabout 2 dg/min and about 8 dg/min. The melt index of the polymer resinscan be measured using ASTM D-1238.

The term “silane-grafted,” as used herein, means attaching one or moresilicon-containing monomer or polymer to the original polymer chains.The grafting is generally accomplished by forming active grafting siteson the original polymer chains in the presence of silicon-containingmonomers, which can further polymerize as branches from the originalpolymer chains. Active grafting sites can be generated, for example, byfree radicals or anions.

Foams for use in tape applications are generally closed-cell foams. Theterm “closed-cell,” as used herein, means that the greater thanapproximately 70% of the form cell volumes have cell walls isolatingthem from the external atmosphere. One way to determine this is bymeasuring the amount of water that is absorbed into the foam when thefoam is immersed in water.

The invention can have one or more of the following advantages. Thepolymer tapes can have improved flexibility, tensile strength,elongation, and compression set properties. The polymer tapes have goodadhesion properties with traditional adhesives. The polymer tapes can beeasily coated with these adhesives and can be foamed easily. Flexibilitycan be measured, for example, by compressing the foam by 25 percent andmeasuring the force it takes to compress the foam.

The polymer tapes, and foamed polymer tapes, based on silane-graftedsingle-site initiated polyolefin resins have good flexibility withoutthe addition of other components such as plasticizers, for example. Forexample, plasticizers can leach out of tapes and foamed tapes over time,leading to degradation of the physical properties of the foam. Leachingplasticizers can also adversely affect the properties of the adhesive.The polymer tapes based on silane-grafted single-site initiatedpolyolefin resins do not require plasticizer components to enhance theirphysical properties. The polymer tapes do not contain sulfur orchlorine-containing materials.

The polymer tapes, and foamed polymer tapes, have good physicalproperties such as tensile strength, elongation, compression resistance(compression deflection), compression set, and tear resistance. Thesefoam properties can be measured according to ASTM D-3575.

Other features and advantages of the invention will be apparent from thefollowing detailed description thereof, and from the claims.

DETAILED DESCRIPTION

The polymer tape is a polyolefin resin or polyolefin-blend including atleast one silane-grafted single-site initiated polyolefin resin. Thepolymer tape can be foamed. The single-site initiated polyolefin resinsare derived from ethylene polymerized with at least one comonomerselected from the group consisting of at least one alpha-unsaturatedC₃-C₂₀ olefin comonomers. Preferably, the alpha-unsaturated olefinscontain between 3 and 16 carbon atoms, most preferably between 3 and 8carbon atoms. Examples of such alpha-unsaturated olefin comonomers usedas copolymers with ethylene include, but are not limited to, propylene,isobutylene, 1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene,1-octene, 1-decene, 1-dodecene, styrene, halo- or alkyl-substitutedstyrene, tetrafluoroethylene, vinylcyclohexene, andvinylbenzocyclobutane.

The comonomer content of the polyolefin resins is generally betweenabout 1 mole percent and about 32 mole percent, preferably between about2 mole percent and about 26 mole percent, and most preferably betweenabout 6 mole percent and about 25 mole percent.

The copolymer can include one or more C₄-C₂₀ polyene monomers.Preferably, the polyene is a straight-chain, branched chain or cyclichydrocarbon diene, most preferably having between 6 and 15 carbon atoms.It is also preferred that the diene be non-conjugated. Examples of suchdienes include, but are not limited to, 1,3-butadiene, 1,4-hexadiene,1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene,3,7-dimethyl-1,7-octadiene, 5-ethylidene-2-norbornene, anddicyclopentadiene. Especially preferred is 1,4-hexadiene.

The preferred single-site initiated polyolefin resins include eitherethylene/alpha-unsaturated olefin copolymers orethylene/alpha-unsaturated olefin/diene terpolymers.

Preferred single-site initiated polyolefin resins are described, forexample, in S.-Y. Lai, et al., U.S. Pat. Nos. 5,272,236, 5,278,272, and5,380,810, in L. Spenadel, et al., U.S. Pat. No. 5,246,783, in C. R.Davey, et al., U.S. Pat. No. 5,322,728, in W. J. Hodgson, Jr., U.S. Pat.No. 5,206,075, and in F. C. Stehling, et al., WO 90/03414, each of whichis incorporated herein by reference. The resins contain varying amountsof short-chain and long-chain branching, which depend, in part, on theprocessing conditions.

Some single-site initiated polyolefin resins are available commerciallyfrom Exxon Chemical Company, Houston, Tex., under the tradename Exact™,and include Exact™ 3022, Exact™ 3024, Exact™ 3025, Exact™ 3027, Exact™3028, Exact™ 3031, Exact™ 3034, Exact™ 3035, Exact™ 3037, Exact™ 4003,Exact™ 4024, Exact™ 4041, Exact™ 4049, Exact™ 4050, Exact™ 4051, Exact™5008, and Exact™ 8002. Other single-site initiated resins are availablecommercially from Dow Plastics, Midland, Mich. (or DuPont/Dow), underthe tradenames Engage™ or Affinity™, and include CL8001, CLS8002,EG8100, EG8150, PL1840, PL1845 (or DuPont/Dow 8445), EG8200, EG8180,GF1550, KC8852, FW1650, PL1880, HF1030, PT1409, CL8003, and D8130 (orXU583-00-01). Most preferably, the single-site initiated polyolefinresins are selected from the group consisting of Exact™ 3024, Exact™3031, PL1845, EG8200, and EG8180.

The polymer tape can include blends containing single-site initiatedpolyolefin resins and other polymer resins. The single-site initiatedpolyolefin resin can be silane-grafted before blending with otherpolymer resins. Alternatively, the blend itself can be silane-grafted.Examples of other polymer resins include low density polyethylene(LDPE), high density polyethylene (HDPE), linear low densitypolyethylene (LLDPE), ethylene-propylene rubber,ethylene-propylene-diene monomer terpolymer (EDPM), polystyrene,polyvinylchloride (PVC), polyamides, polyacrylates, celluloses,polyesters, polyhalocarbons, and copolymers of ethylene with propylene,isobutene, butene, hexene, octene, vinyl acetate, vinyl chloride, vinylpropionate, vinyl isobutyrate, vinyl alcohol, allyl alcohol, allylacetate, allyl acetone, allyl benzene, allyl ether, ethyl acrylate,methyl acrylate, acrylic acid, or methacrylic acid. The polymer blendscan also include rubber materials such as polychloroprene,polybutadiene, polyisoprene, polyisobutylene, nitrile-butadiene rubber,styrene-butadiene rubber, chlorinated polyethylene, chlorosulfonatedpolyethylene, epichlorohydrin rubber, polyacrylates, butyl rubber, orhalobutyl rubber. The rubber material can be peroxide-cured orvulcanized. Preferred resins include LDPE, LLDPE, polypropylene,polystyrene, or ethylene copolymers such as ethylene-vinyl acetatecopolymer (EVA), or ethylene-ethyl acrylate copolymer (EEA). PreferredEVA resins contain between 5 and 15 percent vinyl acetate.

When the polymer tape contains a polymer blend, the blend can contain upto 80 percent of the other polymer resins. Specifically, when the foamcontains EVA, between 20 and 50 percent of the blend with thesingle-site initiated polyolefin resin can be EVA. Some EVA resins arecommercially available from Exxon Chemical Company, Houston, Tex.,Rexene Products Company, Dallas, Tex., and Quantum Chemical Company,Cincinnati, Ohio.

Silane-grafting of the polyolefin resin occurs when the polymer backboneis activated and reacts with a silane reagent to form the graftcopolymer. The silane-graft can include a subsequently cross-linkablemoiety in the graft chain. For example, the cross-linking can occurunder warm, moist conditions when the cross-linkable moiety ishydrolyzable, optionally in the presence of a suitable catalyst. Levelsof cross-linking can be adjusted by varying the amount ofsilane-grafting introduced to the polyolefin resin or the polyolefinresin blend. The silane-grafting occur in a separate process, or duringa continuous blending and extruding process. Silane-grafting isgenerally accomplished by adding azido- or vinyl-functional silanes anda graft initiator to the polyolefin resin or blend. The grafting of thepolyolefin resin or blend can take place, for example, in an extruder.

The graft initiator can be a free radical generating species, forexample, a peroxide. Examples of peroxides include dicumylperoxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-di-(t-butylperoxy)cyclohexane,2,2′-bis(t-butylperoxy)diisopropylbenzene,4,4′-bis(t-butylperoxy)butylvalerate, t-butylperbenzoate,t-butylperterephthalate, and t-butyl peroxide. Most preferably, thegraft initiator is dicumylperoxide or2,2′-bis(t-butylperoxy)diisopropylbenzene.

Azido- and vinyl-functional silanes have the general formula RR′SiY₂, inwhich R represents an azido- or vinyl-functional radical attached tosilicon through a silicon-carbon bond (e.g., composed of carbon,hydrogen, and optionally sulfur, nitrogen and oxygen), each Y representsa hydrolyzable organic radical (e.g., a radical that can be cleaved fromsilicon by the addition of water); and R′ represents a monovalenthydrocarbon radical or a hydrolyzable organic radical.

Azido-functional silane compounds graft onto the polyolefin resinthrough a nitrene insertion reaction. Suitable azido-functional silanesinclude the trialkoxysilanes such as2-(trimethoxysilyl)ethylphenylsulfonyl azide and6-(triethoxysilyl)hexylsulfonyl azide.

Vinyl-functional silane compounds graft to the polymer resin byfree-radical initiated reactions. Suitable vinyl-functional silanesinclude vinyl-functional alkoxy silanes such a vinyl trimethoxy silane(VTMOS) and vinyl triethoxy silane (VTEOS). Generally during grafting,graft initiators such as the peroxides are included with thevinyl-functional silane to perform a hydrogen abstraction from thepolyolefin resin backbone to initiate grafting and polymerization of thevinyl-functional silane.

The graft can include other monomers, such as di- and tri-allylcyanurates and isocyanurates, alkyl di- and tri-acrylates andmethacrylates, zinc dimethacrylates and diacrylates, styrenes, andbutadiene.

The grafted polymer resin can be cross-linked by exposure to moisture toeffect silanol condensation reactions of the hydrolyzable groups of thependant silane-grafts. Cross-linking develops through hydrolysis of thesilane Y groups to form silanols which condense to form siloxanes. Thecondensation of silanols to siloxanes is catalyzed by metal carboxylatessuch as, for example, dibutyl tin dilaurate or dibutyl tin maleate. Themetal carboxylates can be added to the polymer resin mixture beforegrafting, before blending, or before extrusion. The metal carboxylatesare generally added in a liquid form or compounded in a polymer resin.

Most preferably, the silane is VTMOS, that is grafted on to the polymerbackbone by a reaction which is initiated by2,2′-bis(t-butylperoxy)diisopropylbenzene. The most preferred silanolcondensation catalyst is dibutyl tin dilaurate. The cross-linking can beinduced by the presence of atmospheric moisture, steam, or hot water.Cross-linking can take place predominantly (e.g., more than 50% of thepotential cross-linking) prior to expansion (or extrusion) of the foam.Alternatively, the cross-linking can take place predominantly afterexpansion of the foam.

Regardless of the method of cross-linking used, acceptably flexiblearticles, particularly foamed articles, can only be obtained in certainranges of cross-linking density or level, which is related to the amountof silane-grafting in the blend. Too much cross-linking can render thematerial inelastic. In a foam, this can result in less than optimalexpansion and greater than optimal density for a given level of foamingagent. Too little cross-linking can be detrimental to physicalproperties such as compression set properties or thermal resistance, forexample. It is important to choose cross-linking levels that affordmaterials with particular desired properties. The silane-grafting andresulting crosslinks increase the melt strength of the composition. Thecross-linking levels can be determined by establishing the gel contentof the of the composition, for example, by extraction with a solventsuch as xylenes. Polymer tapes can have cross-link densities of over 55percent, most preferably between 20 and 50 percent.

The polymer tapes can be foamed to make foamed tape. The foamed tapesare predominantly closed-cell foams and can be thermoformed. Theexpanding medium, or foaming agents, useful in the practice of thepresent invention, are physical foaming agents or chemical foamingagents. The term “physical foaming agent,” as used herein, means amedium expanding composition that is a gas at temperatures and pressuresencountered during the foaming step. Typically, a physical foaming agentis introduced to the polymer blend in the gaseous or liquid state andexpands, for example, upon a rapid decrease in pressure. The term“chemical foaming agent,” as used herein, means a medium expandingcomposition that is a solid or a liquid under ordinary processingconditions until the composition is decomposed to release gas. Chemicalfoaming agents can be decomposed, for example, at elevated temperatures.

Physical foaming agents include low molecular weight organic compoundsincluding C₁-C₆ hydrocarbons such as acetylene, propane, propene,butane, butene, butadiene, isobutane, isobutylene, cyclobutane,cyclopropane, ethane, methane, ethene, pentane, pentene, cyclopentane,pentene, pentadiene, hexane, cyclohexane, hexene, and hexadiene, C₁-C₅organohalogens, C₁-C₆ alcohols, C₁-C₆ ethers, C₁-C₅ esters, C₁-C₅amines, ammonia, nitrogen, carbon dioxide, neon, or helium.

Chemical foaming agents include, for example, azodicarbonamide,p-p′-oxybis(benzene)sulfonyl hydrazide, p-toluenesulfonyl hydrazide,p-toluenesulfonyl semicarbazide, 5-phenyltetrazole,ethyl-5-phenyltetrazole, dinitrosopentamethylenetetramine, and otherazo, N-nitroso, semicarbazide, sulfonyl hydrazides, carbonate, andbicarbonate compounds that decompose when heated. The preferred foamingagents are chemical foaming agents, such as azodicarbonamide.

The polymer tape generally is in the form of a sheet having a thicknessbetween about 10 mils ({fraction (1/100)} inch) and {fraction (5/16)}inch. The sheet can be slit, die cut, or laminated. The polymer tape canbe partially or extensively cross-linked prior to exiting the die, orcan be extensively cross-linked after exiting the die. The foamed tapecan be partially or extensively cross-linked prior to expansion, or canbe extensively cross-linked after expansion.

The foamed tape can include foam activating agents, which decrease thedecomposition temperature of the chemical foaming agent. Activatingagents include metal salts such as zinc salts, for example, zincstearate or zinc oxide.

Since the foamed tapes have increased melt strength, a smaller cell sizeand higher cell densities can be achieved in the foam. The higher celldensities lead to lower density foams. The foamed tapes have densitiesbetween about 1.5 and about 50 pounds per cubic foot.

Other additives, alone or in combination, can be added to the tapecompositions including antioxidants (e.g., hindered phenolics such asIrganox 1010, phosphites such as Irgafos 168, or polymerizedtrimethyl-dihydroquinoline such as Agerite AK, Resin D or Flectol H),ultra-violet stabilizers, thermal stabilizers, antistatic components,flame retardants, pigments or colorants, and other processing aids. Inparticular, processing aids, such as fluorinated elastomers (Viton,available from DuPont or Dynamar, available from 3M), and anti-blockagents, such as talc, silica or calcium carbonate, are added to thepolymer tape compositions.

The polymer tape, or foamed tape, is coated on at least one face of thefoam with an adhesive. In many cases, the polymer tape, or foamed tape,is a sheet that is coated on both sides with an adhesive for use injoining applications. It is desired that the polymer tape, or foamedtape, have good peel strength, tensile strength, shear strength, andcleavage strength when joining two articles. The tensile strength,elongation, compression resistance (compression deflection), compressionset, and tear strength can be determined, for example, according to theprocedure of ASTM D-3575. The flexibility of the polymer tape is animportant component of these properties.

Adhesives include, but are not limited to, rubber and acrylic adhesives.In general, adhesives are tacky materials. In general, rubber adhesivesare composed of natural or synthetic rubbers that are made tacky by theaddition of other components to the mixture that do not changesubstantially over time. Acrylic adhesives, on the other hand, changechemically over time giving them different adhesion properties. Acrylicadhesives are based on acrylic or acrylate polymers. In general, acrylicadhesives are formulated to optimize particular properties of the tape.

Rubber adhesives can be generally characterized as having high initialadhesion, moderate strength with shear forces, moderate lifetimes,moderate temperature resistance, and fair resistance to ultravioletlight. Acrylic adhesives can be generally characterized as having fairinitial adhesion that increases substantially over its lifetime, highstrength, high temperature resistance, excellent temperature resistance,and excellent resistance to ultraviolet light.

Rubber adhesives can be based, for example, on one or more of thefollowing elastomers including butadiene-acrylonitrile rubber,butadiene-polyacrylate rubber, butadiene-styrene rubber, butyl rubber,chlorinated rubber, chlorobutyl rubber, cyclized rubber, depolymerizedrubber, natural rubber, polybutadiene, polychloroprene, polyisobutylene,polyisoprene, polysulfide polyurethane rubber, reclaimed rubber,silicone rubber, thermoplastic elastomers, and metallocene orsingle-site initiated polyolefins. Rubber adhesives are available, forexample, from H.B. Fuller Company, Jedco Chemical Company, LordCorporation, National Starch and Chemical Company, PPG Industries,Adhesives and Sealants Division, and 3M Company. These adhesives can usewater or organic solvents or combinations thereof as a carrier.

Acrylic adhesives can be based, for example, on one or more of thefollowing acrylic or acrylate polymers including acrylate-vinyl acetatecopolymer, acrylic-ethylene copolymer, acrylonitrile-butadiene-styreneterpolymer, polyacrylate, carboxylic polyacrylate, polyacrylic esters,and polymethylmethacrylate. Acrylic adhesives are available, forexample, from AMS, American Finish and Chemical Company, CliftonAdhesives, Incorporated, Continental Latex Corporation, FindlayAdhesives, Incorporated, H.B. Fuller Company, T.H. Glennon Company,Incorporated, Industrial Adhesives, Jedco Chemical Corporation, KeyPolymer Corporation, National Starch and Chemical Company, and SwiftAdhesives Division of Reichold Chemical.

Tapes can be produced by coating the substrate (in this case, thepolymer tape, or foamed tape) with an adhesive using any of a number ofconventional coating techniques including reverse roll coating, knifeover roll coating, or extrusion coating. optionally, the coatedsubstrate can be passed through an in-line dryer to remove solvent orwater, or to chemically alter the coating. Machinery for coating thesetapes can be purchased from equipment suppliers such as Ameriflex GroupIncorporated, Black Clawson Converting Machinery Corporation, Inta-Roto,Incorporated, Klockner Er-We-Pa, and Wolverine MassachusettsCorporation.

Methods of combining the various ingredients of the composition include,for example, melt-blending, diffusion-limited imbibition, or liquidmixing. Any or all of the ingredients can be pulverized or reduced inparticle-size by other methods prior to use. Melt-blending can beaccomplished in a batchwise process or a continuous process. It ispreferred that the blending be carried out with temperature control.Many suitable devices for melt-blending are known to the art, including,for example, mixers with single and multiple Archimedean-screw conveyingbarrels, high-shear “Banbury” type mixers, and other internal mixers.The object of such blending (or mixing) is to provide a uniform mixture.Components can be introduced to the mixture in a step-wise fashion atany step during the mixing operation. The mixture can include a foamingagent that expands, for example, upon exposure to the sudden release ofpressure or increase in temperature.

One preferred method of providing a sheet object of this inventioninvolves blending the silane-grafted single-site initiated polyolefinresin with EVA, for example, extruding the blend, cross-linking theblend by exposure to moisture, and coating the blend with the adhesive.Alternatively, the blend can be expanded to form a foam by heating ablend including a chemical foaming agent. Typically, once the foam hasbeen expanded, it is coated with the adhesive. The silane-graftedsingle-site initiated polyolefin resin can be prepared in a separateprocess or an independent step.

For example, the single-site initiated polyolefin resin is melt-blendedwith a 20:1 mixture of vinyl trimethoxy silane (VTMOS) anddicumylperoxide in an extruder to effect the grafting of VTMOS onto theresin. This composition is extruded out of a multiple-strand die faceand is then pelletized. The resulting silane-grafted single-siteinitiated polyolefin resin is melt-blended with ungrafted EVA resin andother additives, which can include the chemical foaming agent. Theblending can occur in a single-screw extruder or a twin-screw extruder.The blend is extruded into, for example, a sheet. The sheet is exposedto moisture in a controlled temperature and humidity environment tocross-link the composition. When the composition includes a chemicalfoaming agent, the sheet can be expanded to a foam by passing the sheetthrough an infra-red oven at a temperature sufficient to decompose thechemical foaming agent. The sheet is then coated with an adhesive,before or after foaming.

Alternatively, the single-site initiated polyolefin resin and otherpolymer resins can be blended and silane-grafted in a single step. Theblend can be combined with other components, such as a chemical foamingagent, in a separate step, or in a continuous process after the graftingstep. Cross-linking can take place to a large extent before, during, orafter expanding the foam.

The following specific examples are to be construed as merelyillustrative, and not limitive, of the remainder of the disclosure.

EXAMPLE 1

The grafted resin was prepared by blending and reacting 49 parts ExxonExact™ 4049, 50 parts Exxon LD 319 EVA (9% vinyl acetate) copolymer, 1part of a fluoroelastomer processing aid (3 percent in a LLDPEconcentrate), 0.35 parts vinyl trimethoxy silane, and 0.018 parts2,2′-bis(t-butylperoxy)diisopropylbenzene (Vulcup R). The blend wasextruded at a 400° F. melt temperature and pelletized.

The grafted resin was blended with other components, as listed in TableI. The blend was extruded into a cross-linkable sheet with a thicknessof 0.028 inches and width of 23.5 inches. The melt temperature was heldbelow 300° F. to prevent premature foaming during the extrusion process.The sheet was not foamed in this step.

TABLE I Formulation of the polymer sheet Grafted resin from Example 162.50% 1.2% dibutyl tin dilaurate/1% antioxidant 3.50% (97.8% LDPEconcentrate) 40% Azodicarbonamide 15.5% (60% LDPE concentrate) 23% ExxonLD319 EVA copolymer 10.00% 10% zinc oxide/20% zinc stearate 6.00% (70%LDPE concentrate) 50% titanium dioxide 2.50% (50% LDPE concentrate)

The sheet was exposed to a temperature of 150° F. and an atmosphere witha relative humidity of 90 percent for a period of 24 hours to cross-linkthe sheet. The cross-linked sheet was passed through an oven where itwas exposed to temperatures of 450 to 500° F., causing foaming to occur.The resulting foam (Foam 1) had a density of 4 pounds per cubic foot, athickness of {fraction (1/16)} inch, and a width of 60 inches. Theproperties of Foam 1 are outlined in Table III.

EXAMPLE 2

The grafted resin was prepared by blending and reacting 70 partsDuPont/Dow Engage™ 8200, 25 parts DuPont/Dow Engage™ 8445, 2 parts of afluoroelastomer processing aid (3 percent in a LLDPE concentrate), 3parts 10% silica antiblock (10 percent in a LDPE concentrate), 0.35parts vinyl trimethoxy silane, and 0.018 parts2,2′-bis(t-butylperoxy)diisopropylbenzene (Vulcup R). The blend wasextruded at a 400° F. melt temperature and pelletized.

The grafted resin was blended with other components, as listed in TableII. The blend was extruded into a cross-linkable sheet with a thicknessof 0.040 inches and a width of 9 inches. The melt temperature was heldbelow 300° F. to prevent premature foaming in the extrusion process.This sheet was not foamed in this step.

TABLE II Formulation of the polymer sheet Grafted resin from Example 282.9% 1.2% dibutyl tin dilaurate/1% antioxidant 3.60% (97.8% LDPEconcentrate) 40% azodicarbonamide 7.20% (60% LDPE concentrate) 10% zincoxide/20% zinc stearate 3.80% (70% LDPE concentrate) 50% titaniumdioxide 2.50% (50% LDPE concentrate)

The sheet was exposed to a temperature of 150° F. and an atmosphere witha relative humidity of 90 percent for a period of 24 hours to cross-linkthe sheet. The cross-linked sheet was passed through an oven where itwas exposed to temperatures of 450 to 500° F., causing foaming to occur.The resulting foam (Foam 2) had a density of 9 pounds per cubic foot, athickness of {fraction (1/16)} inch, and a width of 20 inches. Theproperties of Foam 2 are outlined in the Table III.

In comparison testing, the properties of foamed polymer tapes (Foam 1and Foam 2 from Example 1 and Example 2, respectively) containingsilane-grafted single-site initiated polyolefin resins were compared toother foamed polymer tapes of comparable densities based on otherpolymers (EVA, PVC, and EDPM) according to ASTM D-3575. The results arelisted in Table III. In Table III, tensile strength and elongation arereported in the machine direction and cross direction (MachineDirection/Cross Direction). The data on the Pandel, Lauren, and AMRfoams were taken from Pandel bulletin UFI-1-0188, Lauren data sheetbc-0-610, and AMR catalogs, respectively. Data for the Volara foams weremeasured directly. The Pandel compression set is reported at 25%, whilethe others are reported at 50%. The foams containing silane-graftedsingle-site initiated polyolefin resins have good physical properties.

TABLE III Comparison of foam properties Tensile Compression CompressionDensity Strength Elongation Deflection Set Polymer (PCP) (PSI) % (25%,PSI) (%) Foam 1 Silane- 4 136/107 582/552 6 4.2 grafted Valmra EVA 4141/106 299/321 8 13.0 Type EO Volara EVA 4 140/123 328/398 6.7 16.2Type G Foam 2 Silane- 9 360/280 530/610 11 5.1 grafted Pandel PVC 8 35+100+ 1.5-3.5 15 Max. UF-8 Pandel PVC 12 65+ 100+ 2-6 15 Max. UF-12Lauren EPDM 18 185 205 5-9 11.5 BC-0-610 AMR 4119N Neoprene 7-13 60+150+ 2-5

Other embodiments are within the claims.

What is claimed is:
 1. A method of making a polymer tape comprising thesteps of: providing a cross-linkable polymer mixture including at leastone single-site initiated polyolefin resin and a chemical foaming agent;extruding the polymer mixture; and applying an adhesive to the polymermixture.
 2. The method of claim 1, further comprising the step ofsilane-grafting a portion of the polymer mixture.
 3. The method of claim1, further comprising the step of silane-grafting the single-siteinitiated polyolefin resin.
 4. The method of claim 3, further comprisingthe step of expanding the polymer mixture to form a foam.
 5. The methodof claim 4, further comprising the step of cross-linking the polymermixture.
 6. The method of claim 5, wherein the step of cross-linking thepolymer mixture includes exposing the polymer mixture to moisture.
 7. Amethod of making a polymer tape comprising the steps of: providing across-linkable polymer mixture including at least one silane-graftedsingle-site initiated polyolefin resin and a chemical foaming agent;extruding the polymer mixture; and applying an adhesive to the polymermixture.
 8. The method of claim 7, further comprising the step ofsilane-grafting a portion of the polymer mixture.
 9. The method of claim7, further comprising the step of expanding the polymer mixture to forma foam.
 10. The method of claim 7, further comprising the step ofcross-linking the polymer mixture.
 11. The method of claim 10, whereinthe step of cross-linking the polymer mixture includes exposing thepolymer mixture to moisture.